This invention relates to large tilting pad thrust bearings of the type used in the main propulsion unit of a ship or in vertical shaft water pumps, turbines, motors, generators, or the like. Thus thrust bearings used in ships range in size from approximately 12 to 65 inches in diameter. Those used in vertical shaft rotating machinery range in size from approximately 12 to 162 inches in diameter.
Recent advances in hydro-electric machinery design have created a need for improvements in large thrust bearings due to a significant increase in the shaft speed for a given size machine. For example, some large generators which were formerly operated at 100 rpm now operate at 450 rpm. This increase in shaft speed causes the power loss within the bearing to increase sharply, and the resulting increase in pad surface temperature may exceed the operating limits of the pad material. Increased power loss also reduces the efficiency of the machine and requires cooling equipment of increased size to cool the bearings.
In small tilting pad thrust bearings, one method that has been used in the past to cool the bearing is to drill oil ducts in the individual pads proper, the ducts being positioned to direct jets of cool oil against the runner in the spaces between pads. These oil ducts open on their lower ends into a circular oil groove which surrounds the hardened bearing button upon which the pad is tiltably supported in the retainer. Oil ducts are also drilled in the retainer and open into oil grooves which lie under the oil grooves of the pads. The gaps between the circular oil grooves in the pads and the matching circular oil grooves in the retainer are sealed by O-ring seals that surround both oil grooves and make sealing contact with both the pad and the retainer.
In the operation of this type of bearing, oil is pumped through the retainer ducts into the oil grooves in the retainer and flows from there through the oil grooves in the pads to the oil ducts therein and is discharged as jets of oil against the runner in the spaces between pads. This simultaneously lubricates and cools the bearing by replacing the hot oil film on the runner with cooler oil. Further details of this type of bearing are disclosed in U.S. Pat. No. 3,814,487.
Although the above described thrust bearing lubrication and cooling system works well on small thrust bearings, it is quite expensive when applied to large thrust bearings due to the cost of drilling the necessary multiplicity of oil ducts in the individual pads and retainer and machining the oil grooves in the pads and retainer. The cost of drilling ducts and machining circular grooves in large pads and retainers in the range of 12 to 162 inches in diameter is much higher than the cost of performing the same operation on small pads and retainers. Also, with large bearings the supporting structure for the bearing retainer is often not provided by the bearing manufacturer, and therefore, special arrangements have to be made with the manufacturer of the supporting structure to drill suitable oil feed ducts therein when the above described type of bearing lubrication and cooling system is used. In cases where the supporting structure is already built before the bearing is ordered, the provision of the required oil feed ducts in the supporting structure is even more troublesome and expensive. Accordingly, a need exists for a simpler, less expensive lubrication and cooling system which is applicable to large thrust bearings and which does not require modification of the bearing support structure.